Within every digital integrated circuit there is usually one data path between two circuit blocks that requires more time to propagate valid data than any other path between the circuit blocks. The data path that requires the longest time for the data signal to be propagated before it may be sampled is known as the critical speed path of the integrated circuit. Critical speed paths may be slow due, for example, to a greater number of device delays or greater signal travel distances.
The maximum speed at which the digital integrated circuit may operate is limited by the critical speed path in the digital integrated circuit. The reason for this is that the critical speed path presents the longest delay path and the clock rate cannot be increased beyond the point at which the clock cycle time is equal to the propagation delay of signals on the critical speed path.
Since the maximum speed of an integrated circuit is limited by the critical speed path of the integrated circuit, design of an efficient circuit is facilitated by location of the critical speed path. However, in complex modern integrated circuits such as microprocessors there are millions of possible critical speed paths. To locate the critical speed path among the millions of data paths in the integrated circuit, sophisticated design and testing tools are required.